1. Field of the Invention
This invention relates to an electromagnetic clutch assembly, such as for use in controlling the transmission of power from an automobile engine to the refrigerant compressor in an automobile air conditioning system and, more specifically, to the construction of the driven mechanism of an electromagnetic clutch assembly.
2. Description of the Prior Art
FIGS. 1 and 2 show one prior art embodiment of an electromagnetic clutch assembly 10' intended to be coupled to a refrigerant compressor in an automobile air conditioning system. For purposes of explanation only, the right side of FIG. 2 will be referred to as the forward or front end, while the left side of FIG. 2 will be referred to as the rearward or rear end. As shown in FIG. 2, clutch rotor 15, electromagnetic coil 20, housing 21 and bearing 16 generally constitute the driving mechanism 100 of the electromagnetic clutch assembly. Hub 24, leaf springs 27, stopper, plate 28 and annular armature plate 26 generally constitute the driven mechanism 200' of the electromagnetic clutch assembly.
Electromagnetic clutch 10' is coupled to a compressor housing 11 which is provided with a tubular expression 12 surrounding a compressor drive shaft 13. Drive shaft 13 is supported for rotation within the housing 11 along horizontal axis X by bearings (not shown). Axis X is an axis about which hub 24, armature plate 26 and clutch rotor 15 also rotate.
Clutch rotor 15 is made of a magnetic material, such as steel, and comprises an outer annular cylindrical portion 151, an inner annular cylindrical portion 152 and an axial end plate portion 153 which connects the outer and inner annular cylinders 151 and 152 at their forward ends. Thus, an annular U-shaped cavity 17 is defined by portions 151, 152 and 153. A plurality of V-shaped grooves 18 are provided on the outer peripheral surface of outer annular cylindrical portion 151 for receiving a belt (not shown) to couple the rotor 15 to the output of the automobiles engine (not shown). Rotor 15 is rotatably supported on tubular extension 12 of compressor housing 11 by bearing 16 which surrounds the outer surface of tubular extension 12.
Axial end plate portion 153 includes one or more concentric slits 19 which are disposed on one or more concentric circles. These slits 19 define a plurality of annular or arcuate magnetic pieces with the surface of the poles on the axial end plate portion.
Electromagnetic coil 20 is disposed in annular cavity 17 of clutch rotor 15 to supply a magnetic flux (not shown) for attracting armature plate 26 to the axial end plate portion 153 of the rotor 15. The coil 20 is contained within an annular magnetic housing 21. Housing 21 has a U-shaped cross section and is fixed to a supporting plate 22, which is secured to the axial end surface of housing 11 by a plurality of rivets 221. A small air gap is maintained between coil housing 21 and clutch rotor 15.
Hub 24 comprises a tubular member 241 which is secured tightly on the terminal end portion of the drive shaft 13 by forcible insertion. Flange portion 242 extends radially from the front end of tubular member 241 and may be integrally formed with the tubular member or formed separately and affixed by a known securing method, such as welding. The relative rotation between hub 24 and drive shaft 13 is prevented by a key-keyhole mechanism 131 provided at the terminal end portion of drive shaft 13. Hub 24 is further secured to the terminal end portion of drive shaft 13 by nut 25 which is threaded on the terminal end of drive shaft 13.
Annular shim 132 is disposed between a rearward end of tubular member 241 of hub 24 and an annular ridge 132a. Ridge 132a is formed on the outer peripheral surface of the terminal end portion of drive shaft 13. The shim and ridge arrangement allows for the adjustment of air gap "1" between annular armature plate 26 and axial end plate portion 153 of rotor 15.
Annular armature plate 26 is made of magnetic material, is concentric with hub 24, and has a friction surface 26a which faces the friction surface 153a of axial end plate portion 153 of rotor 15. Armature plate 26 has a plurality of elongated apertures 261 disposed on a concentric circle, and is coupled to flange portion 242 of hub 24 by a plurality of leaf springs 27. Each leaf spring is fixed at one end to armature plate 26 by rivet 31, and at the other end to the rearward surface of stopper plate 28. Stopper plate 28 and the other end of each leaf spring 27 are secured to each other and to flange portion 242 through spacing member 30 by rivets 29. By this arrangement, armature plate 26 may move relative to hub 24 along axis X upon the deflection of leaf springs 27.
Thus, when electromagnetic coil 20 is energized, armature plate 26 is magnetically attracted to axial end plate portion 153 of rotor 15. Armature plate 26 will move rearwardly along axis X so that friction surface 26a engages friction surface 153a. This engagement will transmit the engine-driven rotation of clutch rotor 15 through leaf springs 27 and hub 24 to drive shaft 13.
Conversely, when electromagnetic coil 20 is not energized, leaf springs 27 bias armature plate 26 away from rotor 15. Thus, drive shaft 13 is not rotated by clutch rotor 15, and the compressor is not driven.
Since tubular member 241 of hub 24 is tightly secured on the terminal end portion of drive shaft 13, the driven mechanism cannot be easily removed from the drive shaft 13. Therefore, tool 300, shown in FIG. 3, is used to detach hub 24 from the terminal portion of drive shaft 13. Tool 300 includes an L-shaped cylindrical steel bar member 301, a thread rod 302 extending perpendicularly from the longer straight portion 301a of L-shaped member 301, and a circular plate 303 having a threaded hole 303a at its center to receive rod 302. A plurality of radially disposed elliptical slots 303b are bored at equal intervals through circular plate 303. Three identical bolts 304, each having bolt head 304a, shaft region 304b and threaded shaft region 304c along one-third of its length, are loosely held in slots 303b. Movement of the bolt within the shaft is restricted by bolt head 304a and flange portion 304d, formed at the center of shaft region 304b.
Use of tool 300 can be best described with reference to FIGS. 1 and 2. A plurality of identical threaded holes 242a are bored through flange portion 242 of hub 24. Furthermore, a plurality of holes 262 are bored through stopper plate 28 in alignment with holes 242a. Tool 300 is used in the following manner. After detaching nut 25 from the terminal end of drive shaft 13, the bottom end of rod 302 is placed on the outer end surface of drive shaft 13, perpendicularly to the front face of stopper plate 28. Each threaded shaft region 304b of each bolt 304 is aligned with, and screwed into, respective holes 262 and 242a. L-shaped cylindrical bar 301 is turned and threaded rod 302 is screwed through threaded hole 303a to push rearwardly on the terminal end of drive shaft 13. Thus, the driven mechanism, specifically hub 24, moves axially relative to the drive shaft 13 and is thereby detached from the terminal end of the drive shaft.
In the prior art embodiment, water frequently enters the clutch assembly through holes 262 and 242a, accelerating the corrosion of bearing 16. This has been a major disadvantage of the prior art assemblies, causing degradation of clutch performance and shortening of life expectancy.